dont use higher voltage if your not gonna upgrade your internals, just throw away your crappy NICD and get a respectable one or BUILD your own, you can get TWO 1100MAH minis that are a direct replacement for your 600MAH for $32CDN SHIPPED
OR you can go to costco and buy 8 2300MAH NIMH AA Sanyo Cells and make a 7 cell battery for 20 dollars or less
__________________
|